Pneumatic tire for heavy load

ABSTRACT

A pneumatic tire for a heavy load is provided which prevents irregular abrasion generated at the edge of land portions of the tire tread. An irregular abrasion preventing land portion is thus formed at the edge of a land portion, inside the shoulder edge of the tire, whereby the irregular abrasion generated at this portion is prevented.

This application is a divisional of application Ser. No. 08/709,625,filed on Sept 9, 1996, which is a continuation of application Ser. NO.08/364,828, filed Dec. 27, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a pneumatic tire for heavy load whichis adapted to prevent irregular abrasion from being generated at ashoulder-side edge of a land located inside a land of a shoulder edge.

It is necessary to control the shape of a tire when the tire hits theground in order to improve the operativity and abrasion resistance ofthe tire for heavy load having a tread radius and amounts of camber atthe central part of the tread and the shoulder edges.

When the above shape is elliptic, in spite of the favorable operativityand wandering performance, the shoulder edges become easy to slip on theroad surface because of the lower pressure in the vicinity thereof whenthe tire is in touch with the ground, whereby the shoulder edges areeasily and irregularly abraded.

If the shoulder is arranged to be in touch with the ground over a longerdistance so as to increase the touch pressure in the vicinity of theshoulder edge and thus lessen the sliding abrasion, and if the touchinglength at the central part of the tread is maintained at a certain valueto maintain the operativity (linear motion stability, responsecharacteristic of a steering wheel), the touch pressure at a second landcounted from the shoulder edge becomes lower than at the other parts,and therefore the edge of the second land at the side of the shoulder isnot uniformly abraded. This irregular abrasion spreads gradually overthe entire width of the land, leading to punching of the land.

Under these circumstances, forming of a small step-like land has beenproposed to eliminate the irregular abrasion described above (e.g.,Japanese Patent Laid-Open Publication Nos. 2-169305, 2-88312, and2-88311).

However, in the conventional technique, the step-like land is sometimesout of touch with the ground depending on the condition of use(condition of the load), which invites an irregular abrasion at the edgeof the second land seen from the shoulder's edge. In the case where anotch is cut at a part of the second land closer to the center of thetire, it is disadvantageously impossible to avoid the irregular abrasiondue to the twisting force brought about by the notch.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide apneumatic tire for a heavy load which can prevent irregular abrasion ata land portion inside the shoulder edge, particularly, at the edge ofthe second land at the shoulder edge side which is counted from theshoulder edge.

In accomplishing these and other objects, according to one aspect of thepresent invention, there is provided a pneumatic tire for heavy loadcomprising:

an irregular abrasion preventing land formed, via a slim grooveextending in the circumferential direction of the tire, at the shoulderside of a second land counting from the shoulder's edge and

a plurality of inside notches formed at an edge of the second land atthe side where there is, a second main groove,

wherein the irregular abrasion preventing land is generally at the sameheight as the second land, excluding the irregular abrasion preventingland, when the tire is not in use, the abrasion preventing land has awidth which changes along the circumferential direction, such that theabrasion preventing land includes wide parts of a large width and narrowparts of a smaller width in the axial direction of the tire and theinside notches and narrow parts are alternately disposed in thecircumferential direction of the tire.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a first embodiment of the present invention;

FIG. 2 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a second embodiment of the present invention;

FIG. 3 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a third embodiment of the present invention;

FIG. 4 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a fourth embodiment of the present invention;

FIG. 5 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a fifth embodiment of the present invention;

FIG. 6 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a sixth embodiment of the present invention;

FIG. 7 is a partially-enlarged plan view of a pneumatic tire for heavyload according to a seventh embodiment of the present invention;

FIG. 8 is a partially-enlarged plan view of a pneumatic tire for heavyload according to an eighth embodiment of the present invention;

FIG. 9 is a diagram explanatory of the configuration of an irregularabrasion preventing land in the embodiment of the present invention;

FIG. 10 is a diagram explanatory of the positional relationship of theirregular abrasion preventing land in the embodiment of the presentinvention;

FIG. 11A is a perspective view of the tire of FIG. 1;

FIG. 11B is an explanatory diagram of W and W₀ of the tire;

FIG. 11C is an explanatory diagram of W₁, W₂, W₃, W₄, d₀ d of the tire;

FIG. 11D is an explanatory diagram of W₀ and W_(b) of the tire;

FIG. 11E is an explanatory diagram of the shape when the tire comes intouch with the ground;

FIG. 12A is an explanatory diagram of the tire before touching theground;

FIG. 12B is an explanatory diagram of the index of irregular abrasion;

FIG. 13 is an explanatory diagram of the state of abrasion of the tirein any of the embodiments;

FIG. 14 is a partially-enlarged plan view of a tire according to a firstcomparison example;

FIG. 15 is a partially-enlarged plan view of a tire according to asecond comparison example;

FIG. 16 is a partially-enlarged plan view of a tire according to a thirdcomparison example;

FIG. 17 is a partially-enlarged plan view of a tire according to afourth comparison example; and

FIGS. 18A, 18B, and 18C are enlarged plan views of portions of the tiresin different embodiments of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

Preferred embodiments of the present invention will be fully discussedhereinbelow with reference to FIGS. 1-17, 18A, 18B, and 18C.

FIG. 1 indicates a pneumatic tire for a heavy load in accordance with afirst embodiment of the present invention. As shown in FIGS. 1 and 11A,the tire has main grooves 4, 8 extending continuously in thecircumferential direction and lands separated by the main grooves on atread 1 of the tire. More specifically, referring to FIG. 1, a firstland 3, a first main groove 4, a second land 7, and the second maingroove 8 are formed in this order from a shoulde's edge 2 to the centerC of the tread 1. The second land 7 has, at the side of the shoulder, aslim irregular abrasion preventing land 5a separated from a main body 10of the second land 7 by a slim groove 6. The main body 10 is hence theremaining part of the second land 7 with the irregular abrasionpreventing land 5a excluded. Inside notches 11 are formed atpredetermined distance at the edge of the main body 10 at the sidecloser to the center of the tire. The notches are slots or sipes, etc.to ensure the traction. Reference numeral 33 in FIG. 1 denotes a notchedpart in the first land 3.

When the tire is not in use, the above-described irregular abrasion land5a is generally of the same height as the main body 10 and changes inits width in the circumferential direction of the tire. In other words,the irregular abrasion preventing land 5a has such a flat configurationthat the land 5a has wide parts 51a projecting in a generally triangularshape into the main groove 4 and narrow parts 52arecessed in atriangular shape from the main groove, said wide and narrow parts beingcontinuously, alternately arranged. Each wide part 51a is located at 9confronting position to the end of the inside notch 11. The narrow parts52a are alternately positioned between to the end parts of the insidenotches 11, in the circumferential direction of the tire. The reason forthe formation of the wide and narrow parts will be described below. InFIG. 9, when a vehicle turns, a land A which is the part between theadjacent two inside notches 11 and with is a part of the main body 10 isapt to twist in a direction shown by a broken line in FIG. 9 (in theclockwise direction in FIG. 9) or in the opposite direction thereto.Because of the twist, the distortion of a tread rubber at a part B isincreased, generating the irregular abrasion which spreads from the partB to the whole of the land. As such, if the irregular abrasionpreventing land 5 adjacent to the part B is formed wide in thecircumferential direction of the tire to enhance rigidity, thedistortion of the part B is decreased and the difference of thedistortion at the outer side, in the axial direction of the main body10, is reduced. The irregular abrasion can be accordingly prevented. Inother words, since the slim groove 6 is narrow in width, the preventingland 5 is allowed to come in contact with the main body 10 when the tiretouches the ground, so that the aforementioned interaction is effected.

The positional relationship of the narrow parts 52a and the insidenotches 11 will be depicted with reference to FIG. 10. In FIG. 10, areference position for each inside notch 11 in the circumferentialdirection of the tire is set at an outer end 100 in the axial directionof the inside notch 11. Although it is desired that a line 200corresponds to the a center axis of the distance M between the outer end100 and the outer end of the adjacent inside notch 11 as does line 201which is at the center axis of the narrow part 52a of the irregularabrasion preventing land 5, it is allowable if the shifting amount R1therebetween is not larger than 0.3 times, more preferably, not largerthan 0.2 times the distance M of the adjacent inside notches 11. Whenthe shifting amount is larger than the above value, it is impossible toprevent the irregular abrasion caused by the twisting force of the mainbody 10.

More specifically, the first embodiment is of the size as shown in FIG.1 as a specific example. The width of the first main groove 4 is 14 mmand the wide part 51a and the narrow part 52a of the irregular abrasionpreventing land 5a have respectively 4 mm maximum width and 2 mm minimumwidth. The width of the slim groove 6 is 2 mm, the distance between thecenters of the wide and narrow parts 51a and 52a is 20.5 mm, while thedistance from a touching end 30 of the tire in touch with the ground toan outer side edge of the first main groove 4 is 40.5 mm. The distanceto the center of the tire from the touching end 30 is 108 mm. The mainbody 10, the second main groove 8, and the inside notch 11 in thewidthwise direction of the tire are 27.5 mm wide, 10 mm wide, and 14 mmwide, respectively. Moreover, a 2.5 mm-width wide part and a 1 mm-widthnarrow part of the inside notch 11 are 6 mm and 8 mm long in thewidthwise direction of the tire. The inside notch 11 is formed 11.0 mmdeep. The first and second main grooves 4, 8 are 14 mm in depth, whereasthe slim groove 6 is 11 mm in depth. The notched part 33 of the firstland 3 has 1.0 mm width. The tire is 15 mm wide in the circumferentialdirection thereof and 11.0 mm deep. The shoulder edge is 2.0 mm wide and11 mm deep. The distance M between outer ends of the adjacent notches 11in the axial direction is 41 mm. In the first embodiment, the center ofthe narrow part 52a of the preventing land 5a is positioned at thecenter of the distance between the adjacent two inside notches 11.

A pneumatic tire for heavy load according to a second embodiment of thepresent invention will be discussed hereinbelow.

In the second embodiment shown in FIG. 2, many outside notches 31 areformed every predetermined distance at the side of the irregularabrasion preventing land 5a of the main body 10 of the tire of the firstembodiment in FIG. 1. Since the outside notches 31 are alternatelyarranged to the inside notches 11 in the circumferential direction, atwisting part of the land is turned to a partial land D of the land A.The partial land D is smaller than the land A, reducing the distancefrom the part B where the distortion is large to the twisting center, sothat the amount of distortion of the part B is lessened. Therefore, theirregular abrasion at the part B is effectively prevented. An adequateamount of movement is permitted in the vicinity of an outer end E of theoutside notch 31 in the axial direction, and consequently the distortionis not so large as at the above part B. If the number of the insidenotches 11 is increased twice instead of forming the outside notches 31,the rigidity in the middle part of the adjacent inside notches 11 isdecreased so much as to cause missing or loss of rubber, etc.

As is clear from FIG. 10, when a reference position of the outside notch31 in the circumferential direction of the tire is set at an outer end101 of the outside notch 31 in the axial direction, it is desirable thatthe line 200 in the direction of the center axis of the distance Mbetween the outer ends 100 of the adjacent inside notches 11 in theaxial direction agrees with the above outer end 101. However, if theline 200 shifts from the outer end 101, the shifting amount R3 ispreferably not larger than 0.3 times the distance M, more favorably, notlarger than 0.2 times the distance M. It becomes impossible to preventthe irregular abrasion due to the twisting force of the main body 10 ifthe shifting amount R3 exceeds the aforementioned value.

The size of each part in the second embodiment as a specific example isgenerally the same as that of the first embodiment, except that theoutside notch 31 is 14 mm wide in the circumferential direction of thetire and 11.0 mm deep.

FIG. 3 shows a pneumatic tire for heavy load according to a thirdembodiment of the present invention.

An irregular abrasion preventing land 5b in the tire of the thirdembodiment assumes a different shape from that of the preventing land 5aof the first embodiment. That is, an irregular abrasion preventing land5b of the third embodiment is constituted of rectangular, flat irregularabrasion preventing blocks 51b divided by lateral grooves 52bcommunicating with the first main groove 4 and extending in thewidthwise direction of the tire. The irregular abrasion preventingblocks 51b are generally of the same height as the main body 10 when thetire is not in use and are so disposed as to confront the inside notches11 in the circumferential direction.

Referring again to FIG. 10, although it is suitable that the outer end100 of the inside notch 11 agrees with the line 202 in a direction ofthe center axis of the preventing block 51b, the shifting amount R2 ifany is suitably not larger than 0.3 times, more favorably, 0.2 times thedistance M of the adjacent inside notches 11. In the event that thevalue is exceeded, the irregular abrasion as a result of the twistingforce of the main body 10 is impossible to avoid.

The tire according to the third embodiment as a specific example isconstituted generally in the same size as in the first embodiment. Adifference is that the preventing block 51b is 4 mm wide and 20.5 mmlong, and the lateral groove 52b is 4 mm wide and 20.5 mm long. Thecenter of the preventing land 5b is agreed with the outer end of theinside notch 11 in the third embodiment.

FIG. 4 is a pneumatic tire for heavy load according to a fourthembodiment of the present invention.

The tire of the fourth embodiment has many outside notches 31 formedevery predetermined distance at the side of the irregular abrasionpreventing land 5b of the main body 10 of the tire of the thirdembodiment shown in FIG. 3. The outside notches 31 are alternatelydisposed to the inside notches 11 in the circumferential direction ofthe tire. The reason for this arrangement is the same as that describedabove in conjunction with the second embodiment.

Concretely, the fourth embodiment as a specific example is different insize from the third embodiment only in that the outside notch 31 is 14mm wide and 11.0 mm deep.

A pneumatic tire for heavy load according to a fifth embodiment of thepresent invention is illustrated in FIG. 5.

The tire is provided with an irregular abrasion preventing land 5c whichis different in shape from that of the first embodiment. Morespecifically, wide parts 51c of the irregular abrasion preventing land5c which correspond to the preventing blocks 51b of the preventing land5b in the third and fourth embodiments are integrally coupled each otherat narrow parts 52c. When the tire is not in use, the preventing land 5chas generally the same height as the main body 10, with the wide parts51c arranged to confront the inside notches 11 in the circumferentialdirection of the tire.

The size of the tire according to the fifth embodiment of the presentinvention as a specific example is generally the same as that of thefirst embodiment. A different point is that the wide part 51c has 4 mmwidth and 20.5 mm length, and the narrow part 52c has 2.5 mm width and20.5 mm length. In the fifth embodiment of the present invention, thecenter of the wide part 51c is agreed with the outer end of the insidenotch 11.

In FIG. 6 is indicated a pneumatic tire for heavy load according to asixth embodiment of the present invention.

According to the sixth embodiment, many outside notches 31 are formedevery predetermined distance at the side of the irregular abrasionpreventing land 5c of the main body 10 of the tire of the above fifthembodiment shown in FIG. 5. The outside notches 31 and the insidenotches 11 are alternately arranged in the circumferential direction ofthe tire by the same reason as in the second embodiment.

The tire of the sixth embodiment as a specific example is in thestructure of generally the same size as that of the fifth embodimentexcept that each outside notch 31 has 14 mm width and 11.0 mm depth.

A pneumatic tire for heavy load shown in FIG. 7 is in accordance with aseventh embodiment of the present invention.

An irregular abrasion preventing land 5d in the seventh embodiment isdifferent in size from the land 5a of the first embodiment. In otherwords, the irregular abrasion preventing land 5d is formed of manyrectangular flat irregular abrasion preventing blocks 51d divided bylateral grooves 52d communicating with the first main groove 4 andextending along the widthwise direction of the tire. The lateral groove52d has small width. The preventing blocks 51d are generally in the sameheight as the main body 10 when the tire is not in use, and confront theinside notches 11 in the circumferential direction.

The tire of the seventh embodiment as a specific example has generallythe same size as that of the first embodiment with an exception that thepreventing block 5d has 4 mm width and 39 mm length, while the lateralgroove 52d has 4 mm width and 2 mm length. According to the seventhembodiment, the center of the preventing block 51d is agreed with theouter end of the inside notch 11.

A pneumatic tire for heavy load of an eighth embodiment according to thepresent invention is clearly shown in FIG. 8.

The tire has many outside notches 31 formed every predetermined distanceat the side of the irregular abrasion preventing land 51d of the mainbody 10 of the tire in FIG. 7, namely, seventh embodiment. The outsidenotches 31 are alternately disposed to the inside notches 11 in thecircumferential direction of the tire, the reason for which reads thesame as in the second embodiment discussed before.

Although the tire of the eighth embodiment as a specific example hasgenerally the same size as that of the seventh embodiment, the outsidenotch 31 is 14 mm wide.

Referring to FIG. 11B, in any of the foregoing embodiments, supposingthat the distance from the center C of the tire in the widthwisedirection of the tire to the shoulder edge 2 is W and the distance fromthe center C to the center of the irregular abrasion preventing land 5at the side of the shoulder is W₀, the irregular abrasion preventingland 5 (specifically, the wide parts 5a, 51c of the preventing lands 5a,5c in the first, second, fifth, and sixth embodiments, and the irregularabrasion preventing blocks 51b, 51d of the respective preventing lands5b, 5d in the third, fourth, seventh, and eighth embodiments) is sopositioned as to satisfy 0.50≲(W₀ /W)<0.85. The reason for this is thatthe difference in the outer diameter of edges of lands inside 1/4 thewidth of the tread (where W₀ /W=0.50) to the center of the tire is smalland the pressure when the tire comes in touch with the ground is nearlyuniform, hence without necessities to eliminate slipping of the tire bymeans of the edge of the land 5. If (W₀ /W) is not smaller than 0.85,the shoulder land becomes too small in width, losing the rigidity. Inconsequence of this, the tire is unable to take a good grip on theground at the cornering time and the turning performance isdeteriorated.

Further, referring to FIG. 11C, supposing that the width of the land 10excluding the irregular. abrasion preventing land 5 in the second land 7from the shoulder edge 2 is W₁ (or W₂ for the wide parts 51a, 51c of theirregular abrasion preventing lands 5a, 5c in the first, second, fifth,and sixth embodiments and for the irregular abrasion preventing blocks51b, 51d in the third, fourth, seventh, and eighth embodiments), thewidth of the irregular abrasion preventing land 5 is W₂, the width ofthe first main groove 4 from the shoulder edge 2 is W₃, the width anddepth of the slim groove 6 defined between the land 5 and the main body10 of the second land 7 are designated by W₄ and d₀, and the depth ofthe first main groove 4 is d, 1/3≲(d₀ /d)≲1, 0.03≲(W₂ /W₁)≲0.20 andmoreover (W₄ /W₃)≲0.20 are held. It is not effective when the depth d₀is too small. If (W₂ /W₁) is smaller than 0.03, the rigidity of thepreventing land 5 is lowered too much, and therefore the preventing landbends in the axial direction when the tire hits the ground,deteriorating the effect thereof. Meanwhile, in order for the preventingland 5 to work efficiently even when the transverse force is impressedto the turning tire of a turning vehicle, it is more suitable that (W₂/W₁) is 0.1 or larger. If (W₂ /W₁) exceeds 0.2, the difference of therigidity between the land 5 and the main body 10 is decreased, making itimpossible to concentrate the abrasion force on the preventing land 5.Furthermore, even when (d₀ /d) is larger than 1, the effect of thepreventing land 5 hardly changes and the gauge under the bottom of thegroove cannot be made uniform due to the increased depth d₀. The slimgroove 6 is sufficiently useful even in the case where the slim groove 6is formed by being cut by a knife or the like not to have much width.The width W₄ of the slim groove 6 is therefore 3.0 mm or smaller, morepreferably, 2.0 mm or smaller. If the slim groove 6 is wider, the mainbody 10 never comes in touch with the preventing land 5 when the tiretouches the ground, and the interaction described earlier is notfulfilled, making it impossible to prevent the irregular abrasion of themain body 10.

As in FIG. 11D, it is so arranged that the width W_(b) of a secondlongest breaker 15 from the center C of the tire satisfies 0.60≲(W₀/W_(b))≦0.90, because it is not effective to provide the irregularabrasion preventing land 5 in the vicinity of an edge of the secondlongest breaker 15. That is, it is favorable to set the preventing land5 at a region where the rigidity of the breaker of three sheets isconstant.

Referring further to FIGS. 11E and 12A, assuming that Ls indicates thelength of the tire in the circumferential direction when the tire is intouch with the ground at the outermost circumference and L₀ is thelength at the center of the slim groove 6 in the circumferentialdirection of the tire in touch with the ground, the shape of the tire atthis time holds 0.95≲(L₀ /L_(s))≲1.15. The tread radius (TR) is suitably450-700. In the event that the tread radius exceeds 700 or (L₀ /L_(s))is smaller than 0.95, the central part of the second land 7 isirregularly abraded more, resulting in the punching abrasion. If thetread radius is smaller than 450 or (L₀ /L_(s)) is larger than 1.15, theirregular abrasion is brought about large in the vicinity of theshoulder edge 2 and no effect is attained from the preventing land.

When W₅ is the width of the slim groove 6 when the tire is in touch withthe ground and W₄ is the width of the bottom of the groove 6, andmoreover W₄ ' is the width of an opening at the surface of the slimgroove 6, 0≲W₅ <(W₄ '/2) is satisfied in order to maintain the rigidityof the land 5 when the preventing land 5 touches the ground.

Comparative experiments conducted between the first through eighthembodiments of the present invention and a first through fourthcomparison examples will now be depicted below.

The index of irregular abrasion after a 2--2•D 10 ton truck with 11R22.5steel radial tires (1 steel case 90°, four-sheet steel breaker) runs50,000 km is measured. The smaller the index of irregular abrasion is,the less the irregular abrasion is brought about. Specifically, theindex of irregular abrasion represents the amount F of the stepdifference generated at a part of the second land at the side of theshoulder (average value obtained from twice the values measured at 8points of the second land in the circumferential direction), as shown inFIG. 12B. The result of the experiments is shown in Table 1 below.

The first through fourth comparison examples are illustrated in FIGS.14-17 respectively.

According to the first comparison example, unlike the first and secondembodiments wherein the narrow and wide parts are alternately formed asthe preventing land, an irregular abrasion preventing land 55a is shapedin the form of a simple longitudinal band having a predetermined width,for example, 4 mm in the above specific example of the first embodiment,as shown in FIG. 14.

An irregular abrasion preventing land 56a in the second comparisonexample has, as in FIG. 15, wide and narrow parts 57a and 58a similar tothe irregular abrasion preventing land 5a of the first and secondembodiments of the present invention. However, it is different from thefirst and second embodiments that the center of each narrow part 58a ispositioned at the outer end of the inside notch 11. In the specificexample of the first embodiment, the maximum width of the wide part 57ais 2 mm, the minimum width of the narrow part 58a is 2.5 mm, and thedistance between the centers of the narrow and wide parts 57a, 58a is20.5 mm.

In the meantime, an irregular abrasion preventing land 56b according tothe third comparison example, as shown in FIG. 16, has many irregularabrasion preventing blocks 57b divided by lateral grooves 58b, similarto the irregular abrasion preventing land 5b in the third and fourthembodiments of the present invention. The center of the lateral groove58b in the middle of the adjacent preventing blocks 57b is at the outerend of the inside notch 11, which is a difference from the third andfourth embodiments. The preventing block 57b and the lateral groove 58bare each 4 mm wide and 20.5 mm long in the specific example of the thirdembodiment.

An irregular abrasion preventing land 56d in the fourth comparisonexample, as shown in FIG. 17, has many irregular abrasion preventingblocks 57d divided by lateral grooves 58d, similar to the seventh andeighth embodiments of the present invention. However, the center of thelateral groove 58d between the adjacent blocks 57d is set at the outerend of the inside notch 11, not similar to the irregular abrasionpreventing land 5d of the seventh and eighth embodiments. In thespecific example of the seventh embodiment, the preventing block 57d is4 mm wide, 39 mm long, and the lateral groove 58d is 4 mm wide and 2.0mm long.

                  TABLE 1                                                         ______________________________________                                                Embodiments of the Invention                                          No.     1st    2nd    3rd  4th  5th  6th  7th  8th                            ______________________________________                                        Index of                                                                              140    145    130  135  140  145  115  120                            irregular                                                                     abrasion                                                                              Comparison Examples                                                   No.     1st    2nd    3rd  4th                                                ______________________________________                                        Index of                                                                              100     90     95   95                                                irregular                                                                     abrasion                                                                      ______________________________________                                    

The condition of the abrasion of the tire in each of the aboveembodiments is shown in FIG. 13. Indication (a) in FIG. 13 shows thetire not yet used. With the use of the tire, the step difference issequentially increased or decreased, resulting in the abrasion as shownin indications (b) and (c) of FIG. 13. Since the irregular abrasionpreventing land 5 is formed generally in the same height as the mainbody 10, the preventing land 5 is allowed to be in touch with the roadsurface in any using condition, so that the irregular abrasion iseffectively prevented.

In the first through eighth embodiments as above, the irregular abrasionpreventing land 5 of different widths in the circumferential directionof the tire is provided at the second land 7 at the side of the shouldervia the slim groove 6. Moreover, narrow parts of the preventing land 5are alternately arranged to the inside notches in the circumferentialdirection of the tire, or the preventing land 5 is formed of irregularabrasion blocks via the slim groove 6 only at a part where the tire isabraded irregularly in a manner that the blocks confront the insidenotches in the circumferential direction of the tire. Therefore, whilethe tire is not required to be kept extremely in an elliptic shape whentouching the ground, the irregular abrasion at the edge of the secondland at the side of the shoulder which is inside the tire can beprevented. Owing to this feature to prevent the irregular abrasion atthe shoulder edge, the tire never lacks good grip on the occasion ofcornering, assuring smooth running. Moreover, since the width of theirregular abrasion preventing land 5 is changed so as to prevent thesecond land 7 from bending, slipping of the tire due to the bendingforce acting to the second land 7 from the external force through theroad surface can be avoided. It is to be noted here that the effect isparticularly noticeable when any of the above-described embodiments isapplied to a tire of 75% or lower flatness. As the flatness isincreased, the sidewall shows higher rigidity and it is easy that theshape of the tire in touch with the ground is rectangular, or generallyrectangular with curved and recessed in its up-and-down direction.Further, in each of the foregoing embodiments, the tread radius when theair pressure is standard is preferably 450-700 by the reason that0.95≲(L₀ /L_(s))≲1.15 is held thereby to prevent the irregular abrasionat the shoulder and central part of the tire.

The present invention is not limited to the above first through eighthembodiments, but may be embodied in various kinds of forms. Forinstance, the main groove may be formed zigzag, not straight, uponnecessities. The reason is that the mechanism of the second land 7 andthe irregular abrasion preventing land 5 is not changed. Concreteexamples of such different embodiment are indicated in FIGS. 1BA, 18B,and 18C. In FIG. 18A, both the main grooves 4, 8 and the slim groove 6are zigzag, and the irregular abrasion preventing land 5d is providedwith a recessed groove 9 at the side of the shoulder. Meanwhile, in FIG.18B, the main grooves 4, 8 are formed zigzag, whereas the slim groove 6is straight, with no recessed groove 9 in the irregular abrasionpreventing land 5e. FIG. 18C shows an arrangement in which the maingrooves 4, 8 are zigzag, the slim groove 6 is straight and the irregularabrasion preventing land 5f has a recessed groove 9 at the side of theshoulder.

In the constitution of the present invention, the irregular abrasionpreventing land of different widths in the circumferential direction ofa tire is arranged via the slim groove at the second land at theshoulder side. Narrow parts of the preventing land and inside notchesare alternately disposed in the circumferential direction of the tire,or the preventing land is formed of irregular abrasion blocks via theslim groove to confront the inside notches in the circumferentialdirection of the tire. Therefore, even if the touch length of theshoulder is elongated to increase the touch pressure of the shoulderpart and consequently the touch pressure in the vicinity of the secondland becomes insufficient thereby to cause slipping, the irregularabrasion is prevented from being brought about at the edge of the secondland at the side of the shoulder. Both the irregular abrasion of theshoulder and that of the second land are prevented. The tire is notinsufficient to grip the ground at the cornering time which would resultfrom the irregular abrasion, thus ensuring smooth running of a vehicle.Moreover, since the width of the abrasion preventing land is changed ina manner to prevent bending of the second land, the bending force to thesecond land against the external force from the road surface is absorbedby the preventing land, whereby slipping of the second land due to thebending force is prevented.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. A pneumatic tire for heavy load comprising:a tiretread having a shoulder edge and a center, which when viewed from theshoulder edge to the center of the tire, includes a first land portionadjacent to the shoulder edge, a first main groove having outer andinner edges adjacent to the first land portion, an irregular abrasionpreventing land portion which defines the inner edge of said first maingroove, a narrow groove adjacent to the irregular abrasion preventingland portion, and a second land portion having an outside edge definedby the narrow groove and an inside edge defined by a second main groove,the irregular abrasion preventing land portion being divided intoirregular abrasion preventing blocks by lateral grooves; a plurality ofinside slots or sipes at the inside edge of the second land portion; anda plurality of outside slots or sipes formed to extend from the narrowgroove partially into said second land portion, said outside slots orsipes being disposed between the inside slots or sipes and between theirregular abrasion preventing blocks, wherein the irregular abrasionpreventing land portion is generally the same height as the second landportion when the tire is not in use, and the irregular abrasionpreventing blocks are disposed to confront the inside slots or sipes inthe axial direction of the tire, and wherein the first land portiondefines the outer edge of the first main groove to be circumferentiallystraight, the narrow groove is formed circumferentially straight, andthe second main groove is formed circumferentially straight.
 2. Thepneumatic tire for heavy load according to claim 1, wherein 0.03≲(W₂/W₁,)≲0.20 where a width of the second land portion is W₁, and a widthof the irregular abrasion preventing land is W₂.
 3. The pneumatic tirefor heavy load according to claim 1, wherein a width W₄ of the narrowgroove is therefore 3.0 mm or smaller.
 4. The pneumatic tire for heavyload according to claim 1, wherein 1/3≲(d₀ /d)≲1 where a depth of thenarrow groove is designated by d₀, and a depth of the first main grooveis d.
 5. The pneumatic tire for heavy load according to claim 1, whereinsaid outside slots or sipes each have an outer end on the outside edge,and wherein the outer end of one of said outer slots or sipes iscentered circumferentially between adjacent outer ends of inside slotsor sipes which are located a distance M apart such that the outer end ofthe one of outer slots or sipes is not removed from the center of thedistance M between the adjacent outer ends of the inside slots or sipesan amount larger than 0.3 times the distance M.